Because of durability, lightweight and power efficiency, LED (Light Emitting Diode) has been massively applied to various optoelectronic products, such as indicators, illuminators and displays. Traditionally, LED is driven by DC (Direct Current) power. However, the power source available in the daily life environment is AC (Alternating Current) power. Thus, LED needs to be driven by an AC-DC converter and a step-down transformer, which increase the fabrication cost. Further, energy is wasted when AC is converted into DC.
A U.S. Pat. No. 7,531,843 disclosed a LED structure with an AC circuit, wherein the opposite electrodes of at least two LEDs are connected in parallel, and wherein the LEDs are driven by AC to emit light alternatingly according to the electric connection thereof Such a design indeed makes LEDs able to emit light under AC. However, every LED chip can only emit light at one of the semi-cycles of AC. Thus, only one half of LEDs operate at any moment of AC application, and there are always another half of LEDs idle and wasted.
An R.O.C. Pub. No. 201104911 disclosed a LED illumination device, which integrates a plurality of LEDs and a plurality of rectifier elements (Schottky diodes) to form a Wheatstone bridge-like structure, whereby every LED emits light in the complete cycle of AC, whereby is increased the use rate of LEDs, and whereby is promoted uniformity of illumination. However, the LEDs and rectifier elements are integrated in a wire-bonding method, which not only raises the fabrication cost but also increases the layout area of the device. Besides, the wire-bonding process may decrease the reliability of the device.
A U.S. Pub. No. 20110059559 disclosed an AC light emitting device and a method for fabricating the same, wherein a plurality of light emitting elements are formed on a substrate, and wherein a rectifier-dedicated region is formed on the surface of a portion of the light emitting elements, and wherein rectifier elements are formed on the rectifier-dedicated region, and wherein at least four rectifier elements are arranged to form a Wheatstone bridge functioning as a rectification unit, whereby every LED emits light in the complete cycle of AC, and whereby the rectifier elements have higher inverse bias resistance and lower turn-on voltage. However, in the prior art, the rectifier-dedicated layer is fabricated on the light emitting elements with an epitaxial method or a deposition method after the light emitting element has been fabricated. Next, an etching method is used to define the rectifier elements and the light emitting elements. Such a fabrication process is likely to damage the surface of the light emitting elements, degrade the electric performance of the light emitting elements and lower the light efficiency of the light emitting elements.